I would agree with this. I have had the experience, on a Search-and-Rescue roadblock to stop people venturing where a river had burst its banks, of spending half an hour arguing with a couple of young ladies who really thought their half-ton rendered them invincible. They failed to talk me into letting them through to try it. In part, this was because an RCMP member I know who would drive anything, anywhere had gone down to try to ford the stream earlier, in a 4x4, - and turned back without trying.

Sometimes they can occur with relative speed. They are also extremely powerful movements of water. Even a supremely strong swimmer can be washed away from safety, eventually fatigue, or be pulled under by currents. And that's ignoring the debris that would be in the water with you, which could bludgeon you to pieces, pierce you in a thousand unkindly ways, or simply crush you.

A number of ways. Some people genuinely don't know how to swim - this is far more common than you'd think. Some people underestimate the depth or strength of current and get pulled under deeper water by fast currents and can't get out. Some people get hit by debris and either drown because they're unconscious or because they're pinned underwater by the debris. Some people are old, sick, or disabled and can't get out of the water without help that never comes.

Another dangerous aspect of floods is that they lead to massive epidemics. Floodwater is incredibly dirty, and while you are sorrounded with water you might not have any water that you can safely drink.